Balance of water and sodium/countercurrent

Question 1

Regulation of sodium and water

Answer 1

Both are freely filtered, highly reabsorbed, not secretion

Lots of energy used to reabsorb sodium & water

Question 2

sodium and water reabsorption

Answer 2

2/3 of reabsorption of sodium/water occurs in PCT. Rest is under hormonal control in distal tubule & collecting duct.

Question 3

Sodium reabsorption is

Answer 3

active. Occurs all along tubule except descending of Loop of Henle

Question 4

Water reabsorption is

Answer 4

via osmosis(passive)- depends on sodium reabsorption

Question 5

Water freely crosses cell membranes

Answer 5

False

Question 6

Aquaporins

Answer 6

Water requires aquaporins to be transported across cell membrane.
Lots of these on PCT

Question 7

When Na+ is transported from Tubular lumen to Tubular epithelial cell

Answer 7

Decreases local osmolarity in tubular fluid . Water concentration increases in tubular lumen. Water then follows NA+, other ions out of tubular lumen by osmosis. everyone heads to peritubular capillary via bulk flow.

Question 8

stimulates the insertion of aquaporins into apical side of collecting duct cells via a signaling cascade

Answer 8

ADH

Question 9

water permeability in collecting duct step 1

Answer 9

ADH from posterior pituitary binds to a receptor on basolateral membrane of collecting duct

Question 10

Water permeability in collecting duct step 2

Answer 10

Receptor activates adenylyl cyclase, get increase in CAMP (ATP– cAMP)

Question 11

Water permeability in collecting duct step 3

Answer 11

cAMP activates PKA (protein kinase A)

Question 12

Water permeability in collecting duct step 4

Answer 12

PKA phosphorylate proteins that increase rate of fusion of vesicles w/aquaporins (AQP2) into apical membrane

Question 13

Water permeability in collecting duct step 5

Answer 13

H20 gets pulled out of tubular fluid, into epithelial cell

Question 14

Water permeability in collecting duct step 6

Answer 14

H20 passively flow thru AQP3 +4 on basolateral membrane (always there)

Question 15

Inhibits ADH Release

Answer 15

Alcohol

Question 16

Diabetes insipidus

Answer 16

issues w/ ADH synthesis and release. can pee up to 20-25 L/day when not treated

Question 17

Diabetes Mellitus( sugar diabetes)

Answer 17

glucose stays in urine. water follows sugar, stays om filtrate– lots of pee when untreated. issues w/ blood osmolarity, could be deadly.

Question 18

Sodium excreted…

Answer 18

Is equal to sodium filtered minus sodium reabsorbed

Question 19

vasa recta

Answer 19

blood supply that follows loop- reclaims water to keep medullary interstitial fluid concentrated

Question 20

Urea in concentrating medullary fluid

Answer 20

contributes to osmolarity of medullary interstitial fluid

Question 21

In antidiuretic states, urea..

Answer 21

conc in medullary interstitial increase, aiding water reabsorption

Question 22

if you Increase ADH…

Answer 22

increase urea, increase conc of urine

Question 23

fluid in the proximal tubule is ___ compared to the plasma

Answer 23

isoosmotic

Question 24

fluid in the proximal tubule is ____ compared to fluid in the distal tubule

Answer 24

hyperosmotic

Question 25

fluid in the distal tubule is ____ compared to fluid in the descending limb

Answer 25

hypoosmotic

Question 26

fluid in the descending limb is ____ compared to fluid in the nearby interstitial space

Answer 26

isoosmotic

Question 27

fluid in the ascending limb is _______ compared to fluid in the nearby interstitial space

Answer 27

hypoosmotic